The LMS determined the amino acid sequence of about 400 samples. Many of the unknown sequences determined were of endogeneous peptides eluted from human class I and class II molecules. This information has been used to identify potential antigenic T cell epitopes for possible incorporation into vaccines. Some of the other proteins sequenced by the facility were as follows: Group B streptococcal oligopeptidase (D. Pritchard, Univ. Of Alabama at Birmingham); malaria proteins (D. Kaslow, LPD); transcription factors (B. Moss, LVD); calcium sensing receptor (A. Spiegel, NIDDKD); casein kinase II (B. Critchfield, CDC); varicella-zoster virus proteins (H. Kimura, LCI); calicavirus proteins (S. Sosnovtsev, LID); membrane receptor proteins (M. Sitkovsky, LI); rabbit lymphoid proteins (R. Mage, LI); intracellular transport proteins (J. Bonafacino, NICHD). Three monoclonal antibodies (mAb) (SN8, SN8a, and SN8B) were generated by immunizing mice with an antigen preparation that was isolated from cell membranes of B prolymphocytic leukaemia (B-PLL) cells. These SN8 series mAb showed selective reactivity with B-PLL, B non-Hodgkin's lymphoma, and cell membrane Ig (mIg)-expressing B acute lymphoblastic leukaemia (B-ALL) cell specimens among the many different human leukaemia/lymphoma samples tested. Among the various normal human peripheral blood cells tested, only B cells reacted with these mAb. The antigen defined by these mAb was determined by sequence determination to be the human homologues of the murine mb1and B29 proteins (known as Igalpha and beta). Proliferation and differentiation of hematopoietic cells are regulated by growth factors or cytokines in the bone marrow microenvironment. Some of these cytokines are derived from plasma membranes of T- or B- lymphocytes and may shed from the cell surface. One such cytokine membrane burst promoting activity (mBPA), is shown to be a 28 kd membrane glycoprotein that is derived from normal human B-cells and is shed on vesicles from these cell surfaces. We showed a similar activity to be present on a leukemic cell line, A1, a B cell lineage leukemic cell line, derived from a child with acute lymphoblastic leukemia. When irradiated A1 cells were cultured with normal bone marrow cells in presence of recombinant erythropoietin (rhEPO), it stimulated burst forming unit erythroid (BFU-E). In order to determine if other leukemia cells or cell lines also induce similar stimulation, we used different leukemic cell lines and fresh B-cells from patients with chronic lymphocytic leukemia in a bone marrow bioassay. We are in the process of trying to characterize this as yet unidentified cytokine.